100 Fun Facts About Physical Science

Stars are almost pure balls of which state of matter, which makes up over 99% of the visible universe?

Plasma forms when atoms are stripped of their electrons, which is why it conducts electricity and glows in neon signs and lightning bolts.

When Apollo 15's David Scott dropped a hammer and a falcon feather side by side on the Moon, what happened?

They landed together because the Moon has almost no atmosphere, so no drag slowed the feather, exactly as Galileo had predicted centuries earlier.

Lakes freeze from the top down because liquid water is at its densest at roughly what temperature?

4 °C is where water is heaviest, so the colder water near freezing floats on top and ice forms there first, leaving fish alive underneath all winter.

An 80 kg astronaut keeps the same mass on the Moon, but their weight there drops to roughly what fraction of Earth's?

One sixth is the figure because gravity on the Moon is only about 1.6 m/s², which is why astronauts in moonwalk footage seem to bounce across the surface.

Ice is only slightly less dense than seawater, so roughly how much of a floating iceberg sits below the waterline?

About 90% of an iceberg is hidden underwater, which is why 'tip of the iceberg' came to mean the small visible part of a much bigger problem.

Through which of these does sound travel fastest?

Iron carries sound at about 5,100 m/s, because sound moves faster the stiffer the material; fresh water manages only about 1,500 m/s.

Mixing red, green and blue light at full strength, as the pixels of a TV screen do, produces which colour?

White is what all three light primaries add up to, the reverse of paint, where every pigment absorbs some light, so mixing them all heads towards black.

Gravity on the International Space Station is still 90% of Earth's, so why do the crew float?

They are in constant free fall, along with the station itself, which is moving sideways so fast that it keeps missing the Earth as it drops toward it.

Dry ice used for stage fog leaves no puddle because solid carbon dioxide turns straight into gas, a change called what?

Sublimation skips the liquid stage entirely: under ordinary conditions carbon dioxide has no liquid form, so the solid simply vanishes into gas at −78.5 °C.

Which particle's count in the nucleus, the same for all an element's isotopes and ions, fixes its atomic number?

Protons put the periodic table in order: Mendeleev placed tellurium ahead of lighter iodine on chemical instinct, and sorting the elements by proton count later proved him right.

Helium, neon and argon, which almost never form compounds, make up which group on the far right of the periodic table?

Noble gases were long called the inert gases because their full outer electron shells leave them nothing to gain from bonding; the first compound of one was only made in 1962.

Lithium, sodium and potassium, which fizz or even burst into flame when dropped in water, form which group of elements?

Alkali metals get more violent the further down the group you go: potassium reacts violently at room temperature, and caesium explodes even in cold water.

Silicon and germanium, the elements behind computer chips, sit on the periodic table's zigzag line as which class?

Metalloids are only fair conductors of electricity, which is exactly what makes silicon useful: its conductivity can be tuned, the basis of every transistor.

Which chemists' counting unit is celebrated every 23 October from 6:02 am, a nod to the 6.02 × 10²³ particles it holds?

Mole Day grew from one high-school chemistry teacher's classroom celebration: an article on it in The Science Teacher inspired Maurice Oehler to found the National Mole Day Foundation in 1991.

On the pH scale, usually given as running from 0 to 14, pure water at 25 °C sits at which value?

7 is neutral only at 25 °C: warm the water and its neutral point slips below 7, while staying neutral, because more molecules split into ions.

Instant cold packs for sports injuries chill because dissolving ammonium nitrate in water is which kind of process?

Endothermic processes pull heat in from their surroundings, so the pack drops to near freezing moments after the inner water bag is burst.

Platinum in a car's exhaust converter cleans the fumes by playing which chemical role?

Catalysts speed up reactions without being used up, so a converter needs only a few grams of platinum, which is still valuable enough that thieves cut converters off cars.

Galvanised steel, whose coating corrodes in place of the iron beneath it, owes its rust resistance to which metal?

Zinc acts as a sacrificial layer, corroding first so that even a scratched coating keeps protecting the steel, which is why galvanised buckets and railings last for decades.

In table salt, each sodium atom hands one electron to a chlorine atom, forming which type of chemical bond?

Ionic bonds are the pull between the charged ions left behind, which lock into a rigid lattice, so salt forms hard, brittle crystals that shatter rather than bend.

Which property, described by Newton's first law, makes standing bus passengers lurch forward when the bus brakes?

Inertia means the passengers simply keep moving at the bus's old speed while the bus itself slows beneath them, which is also why seat belts exist.

Which of Isaac Newton's laws explains how a rocket accelerates in empty space, where there is nothing to push against?

The third law says every action has an equal and opposite reaction: the rocket throws hot gas backwards, and the gas pushes the rocket forwards just as hard.

A skydiver stops speeding up once air resistance balances their weight; what is this steady top speed called?

Terminal velocity is reached when drag exactly cancels weight, so a skydiver falls at a steady rate until the parachute opens and a far slower balance is struck.

Tripling the gap between two masses cuts their gravitational pull to what fraction?

One ninth, because three squared is nine: gravity thins out over an ever-larger sphere as the distance grows, so it fades fast but never quite reaches zero.

Big Ben's pendulum beats once every two seconds, a rate set chiefly by which property of the pendulum?

Its length sets the beat, which is how Big Ben is fine-tuned: each old penny stacked on the pendulum raises its centre of mass, shortens its effective length and speeds the clock by 0.4 seconds a day.

A sharp knife cuts better than a blunt one because the same push on a smaller edge gives more of what?

Pressure rises as the same force is squeezed onto a smaller patch, which is also why a thumbtack's point sinks into a wall while its flat head does nothing.

A loading ramp is the simplest form of which classical simple machine, of which a screw is a wrapped-around version?

Inclined planes trade distance for force: moving a load up a long gentle slope takes less effort than lifting it straight up, which is why mountain roads switchback.

Which tool is a second-class lever, with the load between the pivot and the effort, just like a wheelbarrow?

Nutcrackers, like bottle openers and wheelbarrows, always multiply force, because the load sits closer to the pivot than your hands do.

By which method of heat transfer does the Sun's energy cross 150 million km of empty space to reach Earth?

Radiation needs no medium, so it alone crosses the vacuum of space. A vacuum flask turns that around: its empty gap blocks conduction and convection, and its silvered walls reflect radiation.

Which spring law is named for the 17th-century English scientist who also coined the biological word 'cell'?

Hooke's law says a spring's stretch is proportional to the force on it, a discovery Robert Hooke first announced as a scrambled Latin anagram to stake his claim.

Which part of the electromagnetic spectrum has the longest wavelengths, some of them larger than a planet?

Radio waves in the AM band reflect off the ionosphere after dark, which is why stations hundreds of miles away can be picked up at night but not by day.

Sound travels through air as which type of wave?

Longitudinal waves squeeze and stretch along their line of travel, like a shove down a Slinky. Earthquakes send them too: the fast P-waves arrive first, giving warning systems seconds before the damaging S-waves hit.

Turning up a speaker's volume increases which property of the sound wave, while leaving its pitch unchanged?

Amplitude is the size of the wave's swings: bigger swings mean more energy and a louder sound, while pitch depends on how many swings pass each second.

Sound above roughly what frequency counts as ultrasound, the range bats and porpoises use to find their prey?

20,000 Hz is roughly the top of a healthy young adult's hearing. Lazzaro Spallanzani found in the 1790s that blinded bats still dodged obstacles, but no one heard their calls until Donald Griffin used an ultrasound detector in 1938.

Which colour of visible light has the shortest wavelength, at about 400 nanometres?

Violet light has the highest frequency our eyes can register; just beyond it lies ultraviolet, which we cannot see but which still burns skin.

A pencil in a glass of water looks bent because light changes speed as it leaves the water, an effect called what?

Refraction is also what lenses, including the ones in your eyes, rely on, and it splits sunlight into a rainbow when raindrops bend each colour by a different amount.

Short-sightedness, where distant objects blur, is corrected with spectacles that use which shape of lens?

Concave lenses spread light out before it enters the eye, pushing the focus back onto the retina. Such spectacles were already being worn, yet nobody could say why they worked until Johannes Kepler explained it in 1604.

Counting from a lightning flash to its thunder, roughly how long does sound take to cover each kilometre?

About 3 seconds per kilometre, so a five-count gap means the strike was well under two kilometres away, and a flash with an instant crack means it was very close.

In which type of circuit do the other lights in a house stay on when one bulb burns out?

Parallel wiring gives every bulb its own loop back to the supply, whereas in a series circuit one dead bulb breaks the path for all of them.

On the decibel scale, a rise of 10 dB means a sound's power has been multiplied by how much?

10 times more power for every 10 dB, because the decibel scale is logarithmic: a 30 dB jump is not three times the power but a thousand times.

Scrapyard cranes lift and drop scrap steel using which device?

Electromagnets pull only while current flows through the coil, so cutting the power lets a crane drop its load, and the same switchable magnetism rings doorbells and drives loudspeakers.

A bicycle dynamo that lights a lamp from the turning wheel is a small version of which power-station machine?

Generators turn motion into electricity, and a motor is the same machine run backwards: spin a motor's shaft by hand and it will produce a current.

Power stations step electricity up to hundreds of thousands of volts before it travels along pylons to reduce what?

Energy loss in the cables falls because a higher voltage means a smaller current for the same power, and it is current that heats the wires.

Heating an iron magnet above about 770 °C, its Curie temperature, does what to it?

It loses its magnetism because the heat jostles its atoms out of alignment, a threshold that Pierre Curie showed every magnetic material has.

Which gas, about a fifth of the air, makes a glowing wooden splint burst back into flame in the classic school test?

Oxygen makes the ember flare because burning is a reaction with it, and the more concentrated the gas, the faster the splint burns and the fiercer the flame.

Flour dust in a mill can explode while bagged flour only smoulders, because grinding a solid hugely increases its what?

Surface area is what a reaction feeds on, and a dust cloud exposes so much of it that a Minneapolis flour mill blew up in 1878, killing 18 people.

Which French chemist, guillotined in 1794, showed that a chemical reaction leaves the total mass of matter unchanged?

Antoine Lavoisier weighed everything going into and out of sealed reactions, and the conservation of mass he confirmed is why chemical equations must balance.

We only ever see one face of the Moon because its spin and orbit take the same time, a state called what?

Tidal locking happens when a planet's gravity tugs on the bulge it raises in a spinning moon until the spin slows to match the orbit. Pluto and its moon Charon have done it to each other, so each always shows the other one face.

A total solar eclipse can happen only at which phase of the Moon, when it passes directly between Earth and the Sun?

New is the only phase with the Moon between us and the Sun, and even then its tilted orbit usually carries its shadow above or below Earth, so totality is rare.

Tungsten bars have been plated to pass as which precious metal, whose 19.3 g/cm³ density tungsten almost matches?

Gold and tungsten differ in density by under half a percent, so a plated tungsten bar passes a weight check. Weeks after the 1983 Brink's-Mat bullion robbery, Vienna police seized ten such bars stamped to pass as the loot.

To coast away from Earth for good on launch speed alone, ignoring air drag, a projectile needs roughly what speed?

11 km/s, some 40,000 km/h, is Earth's escape speed. The Moon's is only 2.4 km/s, and at a black hole's event horizon the figure passes the speed of light, which is why not even light gets out.

Despite the word 'year' in its name, a light-year is a unit used to measure what?

Distance is what a light-year measures: how far light travels in one year, about 9.46 trillion km. Astronomers themselves usually prefer the parsec, which is roughly 3.26 light-years.

The Statue of Liberty turned green within about 20 years because its thin skin is which metal?

Copper weathers to a green crust called verdigris, which shields the metal beneath from further corrosion. When Liberty was unveiled in 1886 she was a shiny reddish-brown.

The 'lead' in a pencil has never contained any lead; it is clay mixed with which form of carbon?

Graphite was taken for a kind of lead when a huge deposit was found at Borrowdale, England, in the 1500s, and the name stuck. The first sticks were simply sawn off and wrapped in string or sheepskin.

Travelling at roughly 300,000 km every second, sunlight still takes how long to reach Earth?

About 8 minutes is the delay, so we always see the Sun as it was that long ago. If it went dark this instant, the sky would stay bright until the last of its light arrived.

Which Austrian physicist imagined a cat in a sealed box that is both alive and dead until observed?

Erwin Schrödinger meant the cat as a jab at ideas he found absurd when he devised it in 1935. It ended up as part of the foundations of quantum mechanics anyway.

Which metal, long used in thermometers, is the only one that stays liquid at room temperature?

Mercury stays liquid down to about −39 °C, which is why it suited thermometers. Gallium comes close: it sits solid on a table but melts in a warm hand.

Which DuPont material was found by accident in 1938, coating the inside of an 'empty' gas cylinder?

Teflon turned up when Roy Plunkett's team sawed the cylinder open and found a waxy, strangely slippery lining. It went on to coat the world's non-stick frying pans.

A candy bar that melted in Percy Spencer's pocket near a radar set in 1945 inspired which appliance?

Microwave oven history began with that melted snack. Spencer next tried popcorn, then an egg, which exploded in a colleague's face, and Raytheon sold the first 'Radarange' in 1947.

What makes the top of the Eiffel Tower lean up to 18 cm away from the Sun on a clear day?

Thermal expansion lengthens the metal on the sunlit side while the shaded side stays shorter, so the summit bends away. The same heat makes the iron tower slightly taller in summer than in winter.

What do physicists call the way an ambulance siren seems to drop in pitch as it speeds past you?

Doppler effect is the name, after Christian Doppler, who proposed it in 1842 to explain the colours of double stars rather than sound. A Dutch scientist tested it on sound three years later.

Which US Founding Father proposed flying a kite in a storm to prove that lightning is electrical?

Benjamin Franklin reportedly flew it in 1752 with a house key tied to the string. A physicist running his own lightning experiment in Saint Petersburg the following year was killed.

In E = mc², often called the world's most famous equation, what does the letter c stand for?

The speed of light is so large, and squared at that, that a little mass equals a vast amount of energy. The Sun turns about four million tonnes of matter into energy every second.

Which Greek is said to have leapt from his bath and run naked through Syracuse crying 'Eureka'?

Archimedes had just realised that the water he displaced could measure the volume of a king's oddly shaped crown. The tale comes from the Roman architect Vitruvius.

The crack of a bullwhip is a miniature version of which noise, also made by jets outrunning sound?

A sonic boom trails a supersonic jet for its whole flight, not just at the instant it passes the sound barrier. That is why Concorde could fly at full tilt only over the ocean.

Window glass is about 70% silica, which glassmakers get by melting which abundant natural material?

Sand rich in quartz is the main ingredient of everyday glass. Nature makes glass from it too: lightning striking a beach or desert can fuse the grains into hollow tubes called fulgurites.

Which gas, used by dentists as a mild anaesthetic, is better known by the nickname laughing gas?

Nitrous oxide got the nickname from the chemist Humphry Davy, after the giddy euphoria it produces when inhaled. It sits on the World Health Organization's list of essential medicines.

Which gas, the lightest and most abundant element in the universe, filled the airship Hindenburg?

Hydrogen was cheap and gave more lift, while the helium the ship was designed for was scarce and costly, made in bulk only in the United States. The airship burned while docking in New Jersey in 1937.

Which gemstone, rated 10 at the top of the Mohs scale, is the hardest natural material known?

Diamond is about four times as hard as corundum, the mineral of rubies and sapphires that sits just one step below it at 9. The scale ranks minerals in order without showing such gaps.

Which Scot adopted 'horsepower' to sell his steam engines and gave his name to the unit of power?

James Watt did not invent the steam engine: he made Thomas Newcomen's design far more efficient by adding a separate condenser. One horsepower equals about 746 of the units named after him.

Explosions in space would be silent because sound, unlike light, cannot travel through what?

A vacuum has no particles to pass a vibration along, so sound stops dead while light crosses it freely. A film's roaring space battle would really play out in silence.

Which Italian scientist lived out his days under house arrest after an Inquisition trial in 1633?

Galileo Galilei had argued that Earth circles the Sun, backed by the four moons he saw orbiting Jupiter through his telescope. The court found him 'vehemently suspect of heresy'.

Which Serbian-American pioneer of AC electricity gave his name to the unit of magnetic flux density?

Nikola Tesla's induction motor patents were licensed by Westinghouse in 1888 and became the cornerstone of its AC system. The unit was named in his honour in 1960, after years in which his work was half forgotten.

Which German physicist took the first Nobel Prize in Physics, in 1901, for discovering X-rays?

Wilhelm Röntgen made one of his first images of his wife's hand; seeing her own bones, she said, 'I have seen my death!' He refused to patent the discovery so that everyone could benefit from it.

A roller coaster racing through the bottom of a drop has turned its stored energy into which type?

Kinetic energy is the energy of motion, from the Greek kinesis. A classic coaster carries no engine: a chain hauls it up the first hill, and the trade between height and speed does the rest.

The Sun shines by forcing light atomic nuclei together into heavier ones, a process known as what?

Fusion needs staggering heat: the Sun's core is close to 15.7 million kelvins. Reactors on Earth, lacking the Sun's crushing gravity, have to run about ten times hotter still.

Which radioactive element did Marie Curie name after her homeland, then split between three empires?

Polonium honours Poland, which in 1898 was partitioned between three neighbouring powers. It was the first element ever identified purely by its radioactivity.

Which Russian chemist left gaps in his 1869 periodic table for elements nobody had yet discovered?

Dmitri Mendeleev also predicted the properties of three of the missing elements. Gallium, scandium and germanium were all found within his lifetime, and they matched.

What name is given to −273.15 °C, a temperature that can be approached but never actually reached?

Absolute zero marks 0 on the Kelvin scale. An experiment in Bremen has chilled matter to 38 trillionths of a degree above it, far colder than the universe's average of about 2.73 K.

Which Swedish astronomer's thermometer scale first had water boiling at 0 and freezing at 100?

Anders Celsius proposed it that way round in 1742. Within a few years others had flipped the scale, among them the botanist Carl Linnaeus, who wanted a thermometer for his greenhouses.

Which Italian built the first electric battery from stacked metal discs and gave his name to a unit?

Alessandro Volta's 'pile' showed that electricity could be made chemically, overturning the belief that only living things produced it. An admiring Napoleon heaped honours on him.

Which gas, the main ingredient of natural gas burned in kitchen hobs, has the formula CH4?

Methane has no smell, so suppliers add a rotten-egg odorant to make leaks obvious. A deadly school explosion in Texas in 1937 prompted the push to require it by law.

Vinegar, whose name comes from the Old French for 'sour wine', owes its bite to which compound?

Acetic acid forms when bacteria turn the alcohol in wine or cider sour, a process Louis Pasteur showed to be the work of microbes. The word 'acetic' itself comes from the Latin for vinegar.

Chlorine in swimming pools and iodine in antiseptic belong to which reactive group of elements?

Halogens means 'salt-formers', because they react with metals to make salts such as table salt. Theirs is the only group whose members include a gas, a liquid and a solid at room temperature.

Which precious metal conducts electricity better than any other but is too costly for house wiring?

Silver also beats every other metal at carrying heat and reflecting light, so thin layers of it go into solar cells and specialised mirrors.

A singer can shatter a wine glass by singing at the glass's natural frequency, thanks to what?

Resonance builds each vibration on the one before, the way a playground swing climbs higher when pushed in time. In the glass, the wobble grows until it fractures.

The sky is blue because air molecules redirect blue sunlight more than red, a process called what?

Scattering also paints sunsets red: light from a low Sun crosses so much air that most of its blue has been knocked aside before it reaches your eye.

Which particle, nicknamed the 'God particle', was detected at CERN's Large Hadron Collider in 2012?

Higgs boson is its proper name, after Peter Higgs, who in 1964 helped propose the mechanism that gives other particles their mass. The search for it lasted some 40 years.

Which handheld detector famously clicks faster and faster as it nears a radioactive source?

Geiger counter clicks each mark one ionising event picked up by its gas-filled tube. The principle dates from Manchester in 1908, but a practical instrument had to wait for a better tube in 1928.

Carbon dating relies on which property of carbon-14, a span of about 5,730 years?

Half-life is the time in which half of a sample decays; after enough of them, so little carbon-14 remains that the method runs out at around 50,000 years. Its inventor, Willard Libby, won the 1960 Nobel Prize in Chemistry.

Which element, named after a then newly discovered planet, is the main fuel of nuclear power plants?

Uranium was named by the chemist Martin Klaproth in 1789, in honour of Uranus. Reactors rely on it because it is the only natural element with a readily splittable form found in useful amounts.

Which former bookbinder's apprentice showed in 1831 that a moving magnet can make electricity flow?

Michael Faraday had little formal schooling, yet his discovery of induction is what lets power stations and transformers work. He also made the Royal Institution's Christmas Lectures popular.

Which New Zealand-born physicist proposed in 1911 that every atom has a tiny central nucleus?

Ernest Rutherford was led to it when particles fired at thin metal foil sometimes bounced straight back. He said it was like firing a 15-inch shell at tissue paper and having it return to hit you.

Albert Einstein's Nobel Prize in Physics honoured his explanation of what, rather than relativity?

Photoelectric effect: in 1905 Einstein argued that light arrives in packets, later named photons, which knock electrons out of metal. The prize citation never mentioned relativity by name.

Which particles did Murray Gell-Mann name after a nonsense word in James Joyce's Finnegans Wake?

Quarks got their name from the line 'Three quarks for Muster Mark!', and Gell-Mann liked that the number three matched how they occur in nature. They come in six 'flavours', from up and down to charm and strange.

Many home smoke detectors contain a speck of which man-made radioactive element, first made in 1944?

Americium was a wartime secret until its co-discoverer Glenn Seaborg let it slip on a children's quiz show in 1945, five days before the official announcement.

Until 2019, which unit was defined by a golf-ball-sized metal cylinder locked in a vault near Paris?

The kilogram's master cylinder sat behind three separately held keys, yet it still seemed to drift by about 50 millionths of a gram in a century against its copies. A constant of nature now fixes the unit instead.

Which English pioneer of atomic theory also wrote the first scientific account of colour blindness?

John Dalton was colour-blind himself, and the condition is still called Daltonism in several languages. Tests on his preserved eyeball in 1995 confirmed which type he had.

By the second law of thermodynamics, which quantity of an isolated system can rise but never fall?

Entropy tracks how spread out and disordered energy has become, and its one-way rise is why spilt coffee never gathers itself back into the cup. Rudolf Clausius coined the word from the Greek for transformation.

Which NASA probe was lost in 1999 after one team's software used metric units and another's did not?

Mars Climate Orbiter flew far too close to the planet because thruster data arrived in pound-force seconds while the navigation software expected newton-seconds, a mismatch by a factor of 4.45.

The Washington Monument was capped in 1884 with a pyramid of which metal, then a costly rarity?

Aluminium was so hard to extract that the 100-ounce cap was the largest piece yet cast. Just two years later a new smelting process sent its price tumbling, and the metal ended up as kitchen foil.